To change date by some filename substrings, I use for example :[=tc.Name:7-8].[=tc.Name:5-6].[=tc.Name:1-4] [=tc.Name:9-10].[=tc.Name:11-12].[=tc.Name:13-14]
It's OK.
But now I want to apply the first day of month to each file, because files are monthly and not day-dated.
I tried
01.[=tc.Name:5-6].[=tc.Name:1-4]
but it is not working.
Each time I use some constant instead or expression as [tc.Name:x-y], result is erratic.
See https://ghisler.ch/board/viewtopic.php?f=3&t=52215&start=15#p366971

Try it with doublequotes directly after "=" of first plugin entry:
[="01."tc.Name:5-6].[=tc.Name:1-4]

This works at least for me

Bingo, sga_wizard. It is working here also.
A big thank.
And sorry : in my previous post I answered to your first answer (deleted by you). Nevertheless I keep that post to show accurately to Christian where is the mistake. So, now Christian has to right that little bug when he has time to do.

The attributes dialog only looks for placeholders when the first character is a "[". This is done because some fields like comments accept any kind of characters, so [ would be prefectly OK in a comment.

The attributes dialog only looks for placeholders when the first character is a "[".
This is done because some fields like comments accept any kind of characters, so [ would be prefectly OK in a comment.

So, an used "[=tc.Name:5-6].[=tc.Name:1-4]"-part is only evaluated, IF the very first sign in that box is an "[" sign.

01/02/2009 (no evaluation/expanding need at all) >>> Set writedate to 02.01.2019 (depending on region, here US?)
03.02.2020 (German format) >>> Set writedate to 03.02.2019
[=tc.Name:7-8].[=tc.Name:5-6].[=tc.Name:1-4] (very first sign is an "[") >>> Set writedate to 29.03.2019
[="01."tc.Name:5-6].[=tc.Name:1-4] >>> Set writedate to 01.03.2019 (trick by sqa_wizard, an literal "01." before placeholder)[=tc.Name:999]01.[=tc.name:-11,2].[=tc.name:-16,4] >>> Set writedate to 01.03.2019 (trick by ghisler(Author) in post below, as "tc.Name:999" will be empty)

This fails to expand the "tc.Names"-parts, because there is no leading "["to switch into that evaluation mode:01.[=tc.Name:5-6].[=tc.Name:1-4] (very first sign is NOT an "[")